1. Field of the Invention
This invention relates to wing configurations for aircraft. More specifically, the invention is an aircraft wing that supports an over-the-wing mounting of an engine nacelle.
2. Description of the Related Art
In aircraft design, engine nacelle geometry and placement has a significant impact on an aircraft's aerodynamics, structural requirements, engine performance, noise levels, maintenance, crash worthiness, passenger comfort, and cost. Balancing all of these criteria/requirements, aircraft designers have traditionally relied on the mounting of engine nacelles either on pylons attached to the underside of an aircraft's wings or attached to the aft portion of the aircraft's fuselage. Another engine nacelle placement option that has been considered is over-the-wing placement. However, the large upper surface pressure disturbances caused by such placement have not made this placement option popular. Thus, it is generally accepted in the art that an efficient-design, under-the-wing pylori-mounted engine nacelle provides the best mounting option for most current engine designs. However, aircraft engine design is moving towards the development of high-bypass ratio turbofans.
Briefly, a high-bypass ratio provides increased efficiency at decreased noise levels, thereby making it desirable to develop and integrate these types of engines into aircraft design. However, high-bypass ratio turbofan engines tend to have relatively large fan diameters. This fact raises new engine nacelle placement issues for aircraft designers trying to use traditional under-the-wing engine placement. These new issues include reduced ground clearance to the bottom of the engine under normal and collapsed nose gear situations, increased foreign object damage susceptibility, increased drag from ever shorter pylons, and greater weight from longer landing gear. Accordingly, aircraft designers have started to explore over-the-wing engine nacelle placement for turbofan engines. For example, FIGS. 1A and 1B illustrate a top and side view, respectively, of an over-the-wing engine nacelle design proposed by D. J. Kinney et al. in “Comparison of Low and High Nacelle Subsonic Transport Configurations,” American Institute of Aeronautics and Astronautics, AIAA-1997-2318, 1997, pp. 806-819. In this design, the aircraft's wing 10 has an unswept inboard section 10A attached to the inboard side of an engine nacelle 20 and has a swept outboard section 10B attached to the outboard side of engine nacelle 20. The leading edge 12 of inboard section 10A is aligned with the point (indicated by reference numeral 22) on the inboard side of engine nacelle that intersects with the sweep line 14A defined by the leading edge 14 of outboard section 10B. The problems with this design are that (i) the shock wave is not confined to the forward part of the airfoil which increases compressibility drag, (ii) there is lift loss due to reduced wing area which raises stall speed and lowers cruise buffet Mach number, (iii) wing bending stress is higher due to a reduction in thickness at the fuselage which increases weight, and (iv) torsional stiffness is reduced due to the reduced airfoil cross section area at the fuselage which lowers flutter speed.